One of the main goals in drug discovery is to identify and develop new ligands with high binding affinity towards a protein target. In some cases the structure of the protein target is known, but in other cases the structure is unknown. A mix of experimental methods and in silico methods is often used for lead identification, and these often make use of automated high-throughput screening (HTS) techniques and combinatorial chemistry. Random screening can be performed using large, diverse libraries, and this can result in identifying a number of lead compounds. However, far more compounds exist (or can be synthesized by combinatorial methods) than can be reasonably evaluated by HTS. Additionally, a number of these lead compounds may fail in the clinical trials phase. Generally, these processes are expensive and time-consuming.